Ultrasonic probes have been used for scanning cellular tissue for many years. Presently, any medical ultrasound examination, whether of the heart, pelvis, abdomen, soft tissues or any other system, is usually displayed as a number of individual frames or pictures from a study performed in a dynamic movie-like manner. The usefulness of the scan, however, is dependent on the skill of the operator, who manipulates the probe by hand while watching the scan images on a monitor to identify areas of interest. Once these areas are identified, the operator usually records single or multiple single scan images showing those areas.
Because the operator must choose a few frames from the large number generated during the scan, the process is open to error. The operator may fail to select an image of an important finding, or may select an image that misrepresents the overall findings. In addition, since the operator is manipulating the probe by hand, and the speed of the probe over the tissue cannot be correlated with the image capture rate of the probe, the coverage of the scanned tissue is somewhat haphazard. As a result, the operator does not record a series of images that represent a contiguous and complete set of images for the entire scanned tissue. Nor does the manual operation of the probe allow for entirely uniform coverage of the tissue, even if multiple passes are used.
A second method of recording ultrasonic examinations is used for dynamic examinations such as echocardiography, where a dynamic recording is made on videotape. Unfortunately, this analog method is not matched to the digital sonographic recording of individual frames. Consequently, there is a great loss of detail that prevents the evaluation of individual frames, which limits the usefulness of the videotape for diagnosing tissue anomalies. In addition, the use of separate videotapes for individual patients is expensive, and creates a storage problem because of the bulkiness of the tapes. The interpreting physician has no way to vary the speed of playback or to vary the size of the images. Nor can the physician vary the inherent contrast and brightness of the images, only the monitor settings. These difficulties lengthen the review time and prevent optimum viewing.
Specific to screening asymptomatic women for occult breast cancer, there are two methods presently in widespread use, physical examination and mammography. Both of these methods are imperfect. Physical examination, whether performed by the woman herself or by a physician or other health care provider, usually cannot detect cancers smaller than ½ inch in diameter. Some cancers have to be many times larger to be detected. Mammography is unable to detect as many as 30 percent of cancers smaller than ½ inch. About 5 to 10 percent of larger cancers are mammographically occult. Mammograms also use radiation and necessitate painful compression of the breasts, which discourage women from having routine mammograms.
Although not well recognized by the medical community, ultrasound is very proficient at diagnosing breast cancers if the location of the abnormality is first discovered by another modality, such as mammography or physical examination. When using ultrasound as a screening method for the entire breast, however, malignancies are usually difficult to pick out of the background tissue. In the past there have been two schemes to use ultrasound for breast screening, but they failed to gain acceptance due to their unacceptably low success rate in finding cancers.
One method was a water bath system with multiple ultrasound probes and the breast in a water bath that allowed generation of images of the whole breast in consecutive slices. These slices could be viewed in sequence at a rate of one every ten seconds.
The second method was to videotape-record the scanning performed by a technician examining the entire breast. This method had the disadvantage of being somewhat haphazard in breast coverage. The variable speed of manual motion does not allow the tissue to be uniformly imaged because the speed is not synchronized to the frame capture rate of the ultrasound probe. Videotaping also results in a degradation of the images for the reasons described above.
To date, no method has been developed to uniformly and reliably use ultrasound probes to create a contiguous and complete set of scan images for an entire area of cellular tissue, such as a human breast. Ultrasound is usually used to investigate areas of interest in cellular tissue that have already been identified by other screening methods such as mammograms, x-rays, and MRI-scans. Ultrasound is not ordinarily used as a screening tool for cellular tissue anomalies.